GHSA-4V6X-C7XX-HW9F
Vulnerability from github – Published: 2026-03-06 23:27 – Updated: 2026-03-20 21:26Impact
The DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing >. For example, <script\n> would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input.
All applications using the DisallowedRawHtml extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected.
Patches
Fixed in 2.8.1. The regex character class [ \/>] was changed to [\s\/>] to match all whitespace characters that browsers accept as valid tag name terminators.
Workarounds
- Set the
html_inputconfiguration option to'escape'or'strip'to disable all raw HTML, though this is a broader restriction than theDisallowedRawHtmlextension provides. - Pass the rendered HTML through a dedicated HTML sanitizer before serving it to users (always recommended)
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 2.8.0"
},
"package": {
"ecosystem": "Packagist",
"name": "league/commonmark"
},
"ranges": [
{
"events": [
{
"introduced": "2.0.0"
},
{
"fixed": "2.8.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-30838"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": true,
"github_reviewed_at": "2026-03-06T23:27:03Z",
"nvd_published_at": "2026-03-07T16:15:56Z",
"severity": "MODERATE"
},
"details": "### Impact\n\nThe `DisallowedRawHtml` extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing `\u003e`. For example, `\u003cscript\\n\u003e` would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input.\n\nAll applications using the `DisallowedRawHtml` extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected.\n\n### Patches\n\nFixed in 2.8.1. The regex character class `[ \\/\u003e]` was changed to `[\\s\\/\u003e]` to match all whitespace characters that browsers accept as valid tag name terminators.\n\n### Workarounds\n\n- Set the `html_input` configuration option to `\u0027escape\u0027` or `\u0027strip\u0027` to disable all raw HTML, though this is a broader restriction than the `DisallowedRawHtml` extension provides.\n- Pass the rendered HTML through a dedicated HTML sanitizer before serving it to users ([always recommended](https://commonmark.thephpleague.com/2.x/security/#additional-filtering))",
"id": "GHSA-4v6x-c7xx-hw9f",
"modified": "2026-03-20T21:26:30Z",
"published": "2026-03-06T23:27:03Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9f"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-30838"
},
{
"type": "WEB",
"url": "https://commonmark.thephpleague.com/extensions/disallowed-raw-html"
},
{
"type": "PACKAGE",
"url": "https://github.com/thephpleague/commonmark"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N",
"type": "CVSS_V4"
}
],
"summary": "CommonMark has DisallowedRawHtml extension bypass via whitespace in HTML tag names"
}
Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
Loading timeline…
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.